The present invention relates to a polishing machine for polishing wafers, e.g., silicon wafers, glass wafers or.
Conventionally, a polishing machine for polishing the wafers basically has: a wafer holding section; a polishing plate for polishing the wafer, the polishing plate being arranged to face the wafer holding section; a mechanism for moving the wafer holding section close to and away from the polishing plate, so as to make the wafer contact a polishing face of the polishing plate; a pressing mechanism for pressing the wafer onto the polishing face with prescribed force; a driving mechanism for relatively moving the wafer, which has been pressed onto the polishing plate, with respect to the polishing plate by rotary movement and/or swing movement; and a mechanism for supplying a liquid abradant, e.g., slurry. Further, the polishing plate has a polishing member, e.g., cloth, felt, sponge, a short hair brush, which is provided on the polishing face of the polishing plate, which is made of a metal plate or a ceramic plate.
A surface of the wafer, e.g., a silicon wafer for semiconductor devices, or a thin glass plate, can be polished like a mirror face by the conventional polishing machine.
In the conventional polishing machine, the wafer which is pressed onto the polishing plate is moved relative to the polishing plate so as to polish the surface of the wafer. The polishing plate is not only rotated about its own axis but also is swung so as to uniformly abrade the polishing member, e.g., the polishing cloth.
However, by rotating or spinning the polishing plate about its own axis so as to polish the wafer, rotational speed at positions on the wafer is different. Namely, rotational speed at a position close to an outer edge of the wafer is faster than rotational speed at a position close to a center thereof. With the speed difference, the surface of the wafer cannot be polished uniformly. To uniformly polish the wafer, the polishing plate is swung but the swing movement is not executed smoothly. Namely, a speed of the swing movement must be changed at turning points, so the polishing plate is not moved at fixed speed throughout. Therefore, in the conventional polishing machine, flatness of the polished wafer is limited. Further, the polishing member is not abraded uniformly.